Mooring system for a tethered hydrokinetic device and an array thereof

ABSTRACT

A mooring system is disclosed for retaining one or more hydrokinetic devices. The system comprises: a hydrokinetic device that is configured to harness energy from a water current and generate electrical power; at least two anchors; and at least two mooring cables having upstream ends attached to the at least two anchors and downstream ends attached to the hydrokinetic device. A centerline of a mooring angle is substantially aligned with a most frequently occurring water current flow direction.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application claims priority and the benefit thereof from U.S. Provisional Application No. 61/221,676, filed on Jun. 30, 2009, and entitled OCEAN CURRENT TURBINE AND HYDROKINETIC POWER GENERATION APPARATUSES AND RELATED METHODS, ALONG WITH MOORING & YAW ARRANGEMENTS, FURLING ROTOR DEPTH CONTROL, AND MOORING HARNESSES FOR USE THEREWITH, the entirety of which is hereby incorporated herein by reference. This application also claims priority and the benefit thereof from U.S. Provisional Application No. 61/236,222, filed on Aug. 24, 2009, and entitled SELF-CONTAINED VARIABLE PITCH CONTROL ROTOR HUB; METHOD OF MAXIMIZING ENERGY OUTPUT AND CONTROLLING OPERATING DEPTH OF AN OCEAN CURRENT TURBINE; AND VARIABLE DEPTH HYDROPLANE SLED, the entirety of which is also hereby incorporated herein by reference. This application also claims priority and the benefit thereof from U.S. Provisional Application No. 61/328,884, filed on Apr. 28, 2010, and entitled FLOODED ANCHORING SYSTEM AND METHOD OF DEPLOYMENT, POSITIONING AND RECOVERY, the entirety of which is hereby incorporated herein by reference

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates to a method, a system and a device for generating power from the kinetic energy of a fluid current. More specifically, the disclosure relates to a mooring system used to restrain a tethered hydrokinetic device.

2. Related Art

Kinetic energy of flowing water currents represents a significant source of clean renewable energy. The water that comprises the world's oceans, rivers and tidal estuaries is constantly in motion, and in many locations there exist repeatable, consistent and rapidly moving ocean currents with speeds in excess of 1.5 meters-per-second (m/s). Such examples include the Gulf Stream, the Humboldt, the Kuroshio, the Agulhas and others. These currents have their origins in ocean thermal and salinity gradients, Coriolis forces, and other ocean thermal transport mechanisms.

These currents represent “rivers in the ocean” which lie predominantly in continental shelf areas with bottom depths in excess of 300 meters. Such depths necessitate mooring a hydrokinetic device with cables or tethers to upstream anchors fixed to the sea bed. The core of these ocean currents can be as much as 30 kilometers wide and flow in a relatively small range of directions with angular variation approaching plus or minus 30 degrees from a centerline defined by the most frequently occurring direction. Ocean current flow directions that are more angularly displaced from the centerline defined by the most frequently occurring direction are less likely to occur, thereby producing a typical normal distribution, or bell curve, of the frequency of occurrence of given ocean current flow directions at a particular geographic location.

Current hydrokinetic devices are frequently moored with cables that include, for example, a single upstream cable or an upstream cable and a vertical cable. The following U.S. patents and patent application Publication Nos. provide examples of known hydrokinetic devices: Publication Nos. US2005/0121917, US2008/0018115A1, US2008/0050993A1; and U.S. Pat. Nos. 4,025,220 and 4,864,152.

A single upstream cable can result in lateral movement, with the attached hydrokinetic device traversing to port-side or to starboard-side to realign itself with changes in the free stream current flow direction. Such lateral movement of the hydrokinetic device may pose a collision and/or cable entanglement risk to neighboring devices in an ocean current farm array. Accordingly, poor use of the natural resource may have to be made since the deployment area for a plurality of hydrokinetic devices must be large to provide adequate space for the lateral movements of the hydrokinetic devices. Furthermore, the laterally mobile devices may pose an increased hazard to nearby recreational or commercial vessels that may be in the vicinity.

A vertical mooring cable, almost by definition, is intended to restrict the vertical movement of the hydrokinetic device and such a mooring scheme prohibits the device from freely ascending or descending without introducing excessive tension or slack in the vertical mooring cable and further increasing the risk of entanglement.

Other known devices include, for example, the hydrokinetic device disclosed in U.S. Pat. No. 6,091,161, which discloses two parallel upstream mooring cables that are selectively lengthened or shortened by winches onboard the device, which cause the device to yaw and align with the oncoming ocean current flow. International Publication No. WO 2009/004420A discloses an intermediate spring type buoy, which requires winch mechanisms and a spring buoy that sits between the hydrokinetic device and the sea floor anchoring point, thereby requiring a large footprint of the mooring system and reducing the number of devices in a given geographic area.

The present disclosure provides a system and a method for restraining a tethered hydrokinetic device that facilitates maximum power generation by the hydrokinetic device.

SUMMARY OF THE DISCLOSURE

According to an aspect of the disclosure, a method, a system, and a hydrokinetic device are provided for harnessing the kinetic energy of flowing water currents to provide clean, renewable energy, as well as maximizing the energy conversion from kinetic energy to electrical energy.

According to an aspect of the disclosure, a mooring system is provided for retaining one or more hydrokinetic devices. The system comprises: a hydrokinetic device that is configured to harness energy from a water current and generate electrical power; at least two anchors; and at least two mooring cables having upstream ends attached to the at least two anchors and downstream ends attached to the hydrokinetic device, wherein a centerline of a mooring angle is substantially aligned with a most frequently occurring water current flow direction. The system may further comprise: an electrical line that may be attached to one of the at least two mooring cables; a communication line that may be attached to one of the at least two mooring cables; or an intermediary harness that may provide a connection interface between the at least two mooring cables and the hydrokinetic device. The mooring angle may encompass a majority of water current flow directions detected at the location over a predetermined period of time. The intermediary harness may comprises: a yoke that is configured to pivot about a transverse axis; and/or a hinge that is configured to rotate about a vertical axis.

According a further aspect of the disclosure, a mooring system is provided for retaining one or more hydrokinetic devices. The system comprises: at least two mooring cables having upstream ends attached to respective anchors and downstream ends attached to a hydrokinetic device, wherein a centerline of a mooring angle between the at least two cables is substantially aligned with a most frequently occurring water current flow direction. The system may further comprise an intermediary harness that provides a connection interface between the at least two mooring cables and the hydrokinetic device. The intermediary harness may comprise: a yoke that is configured to pivot about a transverse axis; and/or a hinge that is configured to rotate about a vertical axis.

According to a yet further aspect of the disclosure, a mooring system is provided for retaining a hydrokinetic device. The system comprises: a yoke that is configured to support a mooring cable and pivot about a first axis; and a hinge that is configured to support the yoke and connect to a support on the hydrokinetic device, the hinge being further configured to rotate about a second axis. The system may further comprise: at least two mooring cables having upstream ends attached to anchors and downstream ends attached to the yoke. The system may further comprise: an electrical line attached to one of the at least two mooring cables; and/or a communication line attached to one of the at least two mooring cables. The first axis may be substantially perpendicular to the second axis. The yoke may be configured to support at least two mooring cables. The hinge may comprise a cross bar. A centerline of a mooring angle formed between the at least two mooring cables may be substantially aligned with a most frequently occurring water current flow direction. The mooring angle may encompass a majority of water current flow directions detected at a location over a predetermined period of time.

Additional features, advantages, and embodiments of the disclosure may be set forth or apparent from consideration of the following detailed description and drawings. Moreover, it is to be understood that both the foregoing summary of the disclosure, the following detailed description and drawings are exemplary and intended to provide further explanation without limiting the scope of the disclosure.

BRIEF DESCRIPTION OF THE EXHIBITS

The accompanying attachments, including drawings, which are included to provide a further understanding of the disclosure, are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the detailed description serve to explain the principles of the disclosure. No attempt is made to show structural details of the disclosure in more detail than may be necessary for a fundamental understanding of the disclosure and the various ways in which it may be practiced. In the exhibits:

FIG. 1A shows a perspective view of an example of a hydrokinetic device, according to principles of the disclosure;

FIG. 1B shows a side of the hydrokinetic device in FIG. 1A;

FIG. 2 shows an example of a distribution of a frequency of occurrence of water current flow direction for a given area;

FIG. 3A-1 to FIG. 3C-3 show examples of a single point, a dual point, and triple point mooring system, respectively, according to principles of the disclosure;

FIG. 4 shows an example of a mooring system with redundant safety lines, according to principles of the disclosure;

FIG. 5 shows a perspective view of an intermediary harness, according to principles of the disclosure;

FIG. 6 shows an example of a farm array with a plurality of electrical and communication lines attached to the mooring cables; and

FIG. 7 shows an example of the electrical and communication lines near the intermediary harness.

The present disclosure is further described in the detailed description that follows.

DETAILED DESCRIPTION OF THE DISCLOSURE

The embodiments of the disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale, and features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the embodiments of the disclosure.

Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the disclosure, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings.

A “computer”, as used in this disclosure, means any machine, device, circuit, component, or module, or any system of machines, devices, circuits, components, modules, or the like, which are capable of manipulating data according to one or more instructions, such as, for example, without limitation, a processor, a microprocessor, a central processing unit, a general purpose computer, a super computer, a personal computer, a laptop computer, a palmtop computer, a notebook computer, a desktop computer, a workstation computer, a server, or the like, or an array of processors, microprocessors, central processing units, general purpose computers, super computers, personal computers, laptop computers, palmtop computers, notebook computers, desktop computers, workstation computers, servers, or the like. Further, the computer may include an electronic device configured to communicate over a communication link. The electronic device may include, for example, but is not limited to, a mobile telephone, a personal data assistant (PDA), a mobile computer, a stationary computer, a smart phone, mobile station, user equipment, or the like.

A “network,” as used in this disclosure, means an arrangement of two or more communication links. A network may include, for example, the Internet, a local area network (LAN), a wide area network (WAN), a metropolitan area network (MAN), a personal area network (PAN), a campus area network, a corporate area network, a global area network (GAN), a broadband area network (BAN), any combination of the foregoing, or the like. The network may be configured to communicate data via a wireless and/or a wired communication medium. The network may include any one or more of the following topologies, including, for example, a point-to-point topology, a bus topology, a linear bus topology, a distributed bus topology, a star topology, an extended star topology, a distributed star topology, a ring topology, a mesh topology, a tree topology, or the like.

A “communication link”, as used in this disclosure, means a wired, wireless and/or acoustic medium that conveys data or information between at least two points. The wired or wireless medium may include, for example, a metallic conductor link, a radio frequency (RF) communication link, an Infrared (IR) communication link, an optical communication link, or the like, without limitation. The RF communication link may include, for example, WiFi, WiMAX, IEEE 802.11, DECT, 0G, 1G, 2G, 3G or 4G cellular standards, Bluetooth, or the like.

The terms “including”, “comprising” and variations thereof, as used in this disclosure, mean “including, but not limited to”, unless expressly specified otherwise.

The terms “a”, “an”, and “the”, as used in this disclosure, means “one or more”, unless expressly specified otherwise.

Devices that are in communication with each other need not be in continuous communication with each other, unless expressly specified otherwise. In addition, devices that are in communication with each other may communicate directly or indirectly through one or more intermediaries.

Although process steps, method steps, algorithms, or the like, may be described in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of the processes, methods or algorithms described herein may be performed in any order practical. Further, some steps may be performed simultaneously.

When a single device or article is described herein, it will be readily apparent that more than one device or article may be used in place of a single device or article. Similarly, where more than one device or article is described herein, it will be readily apparent that a single device or article may be used in place of the more than one device or article. The functionality or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality or features.

A “computer-readable medium”, as used in this disclosure, means any medium that participates in providing data (for example, instructions) which may be read by a computer. Such a medium may take many forms, including non-volatile media, volatile media, and transmission media. Non-volatile media may include, for example, optical or magnetic disks and other persistent memory. Volatile media may include dynamic random access memory (DRAM). Transmission media may include coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to the processor. Transmission media may include or convey acoustic waves, light waves and electromagnetic emissions, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.

Various forms of computer readable media may be involved in carrying sequences of instructions to a computer. For example, sequences of instruction (i) may be delivered from a RAM to a processor, (ii) may be carried over a wireless transmission medium, and/or (iii) may be formatted according to numerous formats, standards or protocols, including, for example, WiFi, WiMAX, IEEE 802.11, DECT, 0G, 1G, 2G, 3G or 4G cellular standards, Bluetooth, or the like.

In order to maximize the energy conversion performance of a hydrokinetic device and convert the greatest amount of kinetic energy in a moving fluid into useable electrical energy, a mooring system should allow the hydrokinetic device to yaw and change azimuth angle so as to align the axis of the rotor with the free stream current flow direction. As the hydrokinetic device yaws to align with the free stream current flow, the mooring system should prevent lateral movement of the device which may present collision risks to neighboring devices and other hazards. Another important consideration for the mooring system is the vertical force component of the mooring cable tension, referred to as the drowning force, which acts as an apparent weight to drown the hydrokinetic device by pulling it to greater depths. As the angle of the mooring cables with the horizontal (intercept angle) becomes steeper, the drowning force increases. When the hydrokinetic device yaws to align with the current, the drowning force should not be dependent on which direction the device is pointing, since this may cause problems with depth control or maintaining a specified depth.

In addition, ocean currents typically exhibit an inverse velocity shear profile, namely, decreasing speed with increasing depth. This inverse velocity shear profile provides an opportunity to maximize energy output by actively positioning the hydrokinetic device at the operating depth at which the rated speed occurs (“rated speed depth”), so that rated power is continuously achievable from the generator. Given this variable depth operational requirement, the mooring system should allow the hydrokinetic device to freely ascend or descend in a vertical water column, so as to seek and be positioned at a rated speed depth.

Furthermore, the mooring system should allow the hydrokinetic device to continually realign itself with regard to both yaw and pitch, thereby generally promoting the free and unimpeded rotation of the hydrokinetic device in these two axes. While allowing such freedom of motion, the mooring system should also allow the upstream mooring cables to remain generally at a fixed spatial orientation to reduce local bending or crimping in the cables that would tend to decrease the usable life of the mooring cables.

Additionally, the mooring system can provide a relatively efficient means of attaching and routing electrical transmission lines and communication data lines from one hydrokinetic device to the next to collect electrical power and information from each device and transmit the electrical power and data to an onshore (or offshore) location. In the routing and attachment of the electrical cabling, it is important that the mooring system provide support to the lines and not place undue tensions or torsions on the lines that would tend to alter the electrical properties or data transmission characteristics and thereby cause electrical or data losses.

The present disclosure provides a mooring system and method that allows a hydrokinetic device, inter alia, to: yaw with little or no lateral movement, whilst allowing alignment of the axis of a rotor with a free stream direction of the water current to promote maximum energy conversion performance; yaw and change azimuth angle without being accompanied by changing forces and moments that are a function of the direction in which the device is pointing; freely ascend or descend to a specified depth without being impeded by extraneous mooring cables; freely rotate in both yaw and pitch about a mooring attachment point without introducing bending or crimping in the cables that may decrease useable lifetime; and provide a supporting routing and attachment path for associated electrical and data cables.

According to an aspect of the disclosure, a mooring system is disclosed that comprises at least two mooring cables, the upstream ends of which may be attached to an underwater surface (for example, a sea bed, a river bed, a platform, an anchor, or the like) and the downstream ends of which may be attached to a hydrokinetic device. A centerline of the included mooring angle formed between two mooring cables may be aligned with the most frequently occurring ocean current direction. Further, the included mooring angle may be configured to be large enough to include a vast majority of all likely ocean current directions that may occur at the particular location at which the hydrokinetic device is deployed.

Additionally, the mooring system may comprise an intermediary universal joint mooring harness device (or intermediary harness). The intermediary harness may provide a connection interface between the mooring cable downstream ends and the hydrokinetic device. The intermediary harness may be configured to allow freedom of pitch and yaw to aid in the alignment of the axis of a rotor with the free stream direction of the current and, thereby, promote maximum energy conversion performance of the hydrokinetic device. The mooring system may further comprise an upstream harness and a downstream harness, with the intermediary harness located therebetween.

The mooring system is further configured to allow the hydrokinetic device, inter alia, to: freely traverse a vertical water column and seek a depth at which operation is most efficient; provide restraint to the hydrokinetic device such that the drowning force is not a function of the azimuth angle of the device; provide lateral restraint to the hydrokinetic device, prohibiting lateral movement to the port side or the starboard side; allow a plurality of hydrokinetic devices to be moored in patterned deployment arrays while minimizing a chance of collision or cable entanglement between neighboring devices; and provide for the attachment of a plurality of non-tensioned electrical lines and communication lines that may carry electricity and/or data.

FIG. 1A shows an example of a hydrokinetic device 100, according to principles of the disclosure. FIG. 1B shows a side view of the hydrokinetic device 100. The hydrokinetic device 100 may include a hull 118, a rotor 114, a hydrodynamic wing (not shown), an aft mounted electrical generator (not shown), a keel 117, a keel cylinder 119, an intermediary harness 116, and a drag inducer 122. A lifting force of the hydrodynamic wing together with a buoyant force supplied by hull 118 may be configured to support the sum of the weight of the hydrokinetic device 100 and the vertical force component of one or more mooring cables 109 attached to the hydrokinetic device 100. An example of the vertical force (or drowning force) component of the mooring cables 109 is shown as a vector force component arrow 108 for one of the two mooring cables 109. By modulating lift, weight (ballast) and drag, the hydrokinetic device 100 is capable of ascending, descending or remaining at a specified depth, as seen in FIG. 1B, and shown by an arrow 150.

The hydrokinetic device 100 is configured to harness the kinetic energy of the water current flow, such as, for example, an ocean current, a river current, an estuary current, a tidal current, or the like, and drive an onboard power generator (not shown). Electrical energy generated by the power generator may be routed to, for example, neighboring hydrokinetic devices 100, or one or more stations (not shown) located in (or on) the water, or located on (or in) land, to collect the electrical energy from the hydrokinetic device 100 prior to transmitting the electricity to, for example, a utility grid, which may be located on water or land. The one or more electric stations may include a computer (not shown) and a communicator (not shown). The communicator may include, for example, a transmitter, a receiver, or a transceiver (i.e., a transmitter and receiver).

Furthermore, communication signals may be sent between the one or more stations (not shown) and the hydrokinetic device 100, as well as between the hydrokinetic devices 100 themselves, which may be located in, for example, a patterned deployment array as shown in FIG. 6. The communication signals may be carried via communication links between a station and the hydrokinetic device 100 and/or communication links between the hydrokinetic devices 100 themselves. Each of the one or more stations and/or the hydrokinetic devices 100 may be coupled to a network.

The hydrokinetic device 100 may include an onboard main controller (not shown) and an onboard communicator (not shown). The communicator may include, for example, a transmitter, a receiver, or a transceiver (i.e., a transmitter and receiver). The hydrokinetic device 100 may include one or more sensors (not shown) for detecting ambient conditions, such as, for example, water temperature, water pressure, water depth, proximity of objects (such as, for example, of other hydrokinetic devices, mammals, fish, vessels, and the like), speed and/or direction of water current flow, and the like. Further, the rotor 114 may include an onboard hub controller (not shown) and a hub communicator (not shown). The hub communicator may include, for example, a transmitter, a receiver, or a transceiver (i.e., a transmitter and receiver). The one or more sensors may include, for example, temperature sensors, pressure sensors, telemetry sensors, acoustic sensors, Infrared (IR) sensors, radio frequency (RF) sensors, and the like. The onboard main controller and hub controller may each include a computer (not shown).

The hull 118 may include a main pressure vessel, which may provide the main source of buoyancy for the hydrokinetic device 100. Additionally, the hull 118 may include one or more interior ballast tanks (not shown) that can be alternately flooded or purged with water to adjust the weight, as well as the location of the center of gravity of the hydrokinetic device 100. The flooding/purging of the ballast tanks may be carried out by, for example, one or more onboard pumps (not shown) that are configured to operate under the control of the main controller (not shown).

The rotor 114 may include a downstream-mounted horizontal axis rotor having a plurality of rotor blades. The downstream-mounted horizontal axis rotor may include a variable pitch control rotor hub.

The keel 117 may include a ventral keel structure, as seen in FIG. 1A, and the keel cylinder 119.

The rotor 114 and keel 117 may together function to passively align a longitudinal axis 103 of the hydrokinetic device 100 and the coincident rotor axis 120 of the rotor 114 with a water current flowing in the direction of C′.

The intermediary harness 116 may be attached to the hydrokinetic device 100 at, for example, a forward position on the keel 117. The intermediary harness 116 is configured to allow the hydrokinetic device 100 to freely yaw about a vertical axis 104 and freely pitch about a horizontal axis 121. One or more mooring cables 109 may be attached to the intermediary harness 116. Each of the mooring cables 109 may exert a force on the intermediary harness 116 that includes three vector components, including a transverse force vector component 106, a forward force vector component 107, and a vertical force vector component 108.

Based on previously acquired water current resource data, including, for example, historical water current direction of flow information at the intended deployment location, a sea bed axis 102 may be determined and designated as the most commonly occurring water flow direction C from available historical data for the particular location. An axis 105 also may be determined, which is perpendicular to the sea bed axis 102. A pair of anchors 112 may be positioned as shown and the length of each of the mooring cables 109 attached thereto may be chosen such that the mooring cables 109 inscribe a mooring angle 111 when attached to hydrokinetic device 100. The two anchors 112 also may be positioned such that the centerline 131 of mooring angle 111 is coincident with the most frequent flow axis 102 denoted by arrow C. A half-angle of the mooring angle 111 may be selected and sized such that the half-angle is substantially equal to, or slightly less than a largest observed variation from the most commonly occurring flow direction based on the historical data at the intended location of deployment.

During operation, and with the water current flowing in the direction C′, the hydrokinetic device 100 may passively yaw to a port side through an azimuth angle 101 and align itself with the longitudinal axis 103 and rotor axis 120 coincident with the water current flowing in the direction C′. As long as the azimuth angle 101 remains less than, for example, the half-angle of the mooring angle 111, the hydrokinetic device 100 may remain in the same location and will not likely move laterally, since the lateral force components 106 of each of the mooring cables 109 will substantially oppose each other, as seen in the vector force diagram in FIG. 1A.

In the event that the azimuth angle 101 exceeds the half-angle of the mooring angle 111, the hydrokinetic device 100 may move laterally. In this case, the rotor 114 may be disengaged from the water current flow with the use of, for example, a variable pitch control rotor hub or other disengagement mechanism to avoid a collision with, or cable entanglement risk to neighboring devices in, for example, an ocean current farm array. As the hydrokinetic device 100 yaws in response to changes in the direction of the water current flow, the drowning force 108 is invariant given the relative constancy of a mooring cable intercept angle 151 (shown in FIG. 1B) over the range of azimuth angles expected to be encountered. Since the drowning force 108 may be a large part of the vertical force balance required to keep the hydrokinetic device 100 at a specified depth, variations in the drowning force 108 that may result from azimuth angle changes may require compensating, laborious and unnecessary changes to weight (or ballast) or hydrodynamic lift to keep the vertical force balance at a substantially net sum zero to remain at the specified depth. Variations in the drowning force with azimuth angle changes are further described with reference to FIGS. 3A-1 to 3C-3.

The hydrokinetic device 100 may include, for example, the hydrokinetic device disclosed in co-pending U.S. patent application Ser. No. ______ (Attorney Dkt. No. 2056997-5004US), filed on the same date as the instant application, and entitled PITCH, ROLL AND DRAG STABILIZATION OF A TETHERED HYDROKINETIC DEVICE, the entire disclosure of which is hereby incorporated herein by reference for all purposes as if fully set forth herein.

The hydrokinetic device 100 may include the variable control rotor hub disclosed in co-pending U.S. patent application Ser. No. ______ (Attorney Dkt. No. 2056997-5005US), filed on the same date as the instant application, and entitled VARIABLE CONTROL ROTOR HUB WITH SELF-CONTAINED ENERGY STORAGE RESERVOIR, the entire disclosure of which is hereby incorporated herein by reference for all purposes as if fully set forth herein.

The hydrokinetic device 100 may be operated using a power control protocol disclosed in co-pending U.S. patent application Ser. No. ______ (Attorney Dkt. No. 2056997-5007US), filed on the same date as the instant application, and entitled POWER CONTROL PROTOCOL FOR A TETHERED HYDROKINETIC DEVICE AND AN ARRAY THEREOF, the entire disclosure of which is hereby incorporated herein by reference for all purposes as if fully set forth herein.

FIG. 2 shows an example of a distribution of a frequency of occurrence of each ocean current flow direction that may be expected to occur at a particular deployment location based on historical data for the location, or nearby locations. The historical data may include, for example, actual ocean current flow data obtained using, for example, an acoustic Doppler current profiler (ADCP) near a core of a well established ocean current over a predetermined period of time (for example, days, months, years, decades, or the like). In FIG. 2, the most frequently occurring current flow direction is noted as C, and the other current flow directions that occur, are noted as C′ and C″, which are less likely to occur—becoming increasingly less likely to occur with greater angular variations in the flow direction of the water current.

Given the above-described ocean current flow directional behavior, the mooring system according to the present disclosure may include at least two mooring cables 109. The upstream ends of the mooring cables 109 may be attached to the anchors 112 and the downstream ends of the mooring cables 109 may be attached to the hydrokinetic device 100—more particularly, the intermediary harness 116. The centerline 131 of the mooring angle 111 between the at least two cables 109 may be aligned with the most frequently occurring ocean current direction C. Additionally, the mooring angle 111 may be configured to be large enough that it encompasses the majority of all likely ocean current directions that may occur at the location of installation, including directions C′ and C″ (shown in FIG. 2).

FIG. 3A-1 to FIG. 3C-3 show examples of a single point, a dual point, and triple point mooring system, respectively, according to principles of the disclosure.

Referring to FIGS. 3A-1 to 3A-3, a single point mooring arrangement is provided for a hydrokinetic device 300. As seen, the hydrokinetic device 300 is anchored to an anchor 303. In this regard, the anchor 303 provides an attachment point for a single upstream mooring cable 302, which is the primary means of restraining the hydrokinetic device 300 from, for example, washing downstream. The upstream mooring cable 302 is attached to hydrokinetic device 300 with the mooring cable intercept angle 310 (shown in FIG. 3A-2), which is the angle formed between the mooring cable 302 and a horizontal reference. The water current is shown flowing in the direction C, with a possible change in direction to direction C′. The single point mooring arrangement allows the hydrokinetic device 300 to move laterally, as shown by a distance 305, as the ocean current changes direction from C to C′.

For example, if the hydrokinetic device 300 is moored at a depth of 350 meters from a sea bed, with a 25 degree mooring cable intercept angle 310, and the ocean current is capable of plus or minus (+/−) about 30 degrees of directional variation, the single point moored hydrokinetic device 300 may move laterally more than about 700 meters from a maximum port side portion to a maximum starboard side position. Such large lateral movements may be problematic and increase the risk of collision to neighboring device, as well mooring cable entanglement. Furthermore, the large lateral movements may complicate servicing the hydrokinetic device 300, which may be in a semi-submerged condition on the surface as the device changes location, thereby increasing hazards to navigation by recreational and commercial vessels in the vicinity, since precise locations of the hydrokinetic device 300 are not likely to be known. The large lateral movements may also complicate the navigational chart cartographers' jobs, since an ‘X’ cannot be precisely located on nautical charts. In an ocean current farm array with single point moorings, as shown in FIG. 3A-3, the array may not only occupy the geographical area required when the ocean current flow direction is in the direction C, but also the additional geographical spaces required when the flow direction is in the direction C′, with all (or most) of the devices having moved laterally by the distance 305. This additional geographic space requirement may be a poor use of the natural resource and will lead to less energy production per unit of geographical area.

Referring to FIGS. 3C-1 to 3C-3, a triple point mooring arrangement is provided for the hydrokinetic device 300. As seen, the hydrokinetic device 300 is anchored to three separate anchors 303. In this regard, the anchors 303 provide attachment points for three separate mooring cables, including a primary upstream mooring cable 302 and a pair of lateral mooring cables 304. As seen in FIG. 3C-2, the upstream mooring cable 302 is attached to hydrokinetic device 300 with the intercept angle 310 and the lateral mooring cables 304 are attached to hydrokinetic device 300 with the intercept angle 312, which as shown is steeper than the intercept angle 310.

While the hydrokinetic device 300 may remain in a substantially fixed position as it yaws about the triple point mooring arrangement shown in FIGS. 3C-1 to 3C-3, the magnitude of the drowning force, which is an important component of the vertical force balance required to maintain a specified depth, may unnecessarily fluctuate with the azimuth angle, thereby requiring the hydrokinetic device 300 to alter weight (or ballast) or hydrodynamic lifting forces to remain at a specified depth. Furthermore, as ocean current speeds change, the hydrokinetic device 300 requires freedom to ascend or descend for various operational advantages and, in doing so, the lateral mooring cables 304 may become slack and even assume a catenary condition, increasing the risk of mooring cable (or line) entanglement.

Referring to FIGS. 3B-1 to 3B-3, a preferred dual point mooring arrangement is provided for the hydrokinetic device 300. As seen, the hydrokinetic device 300 is anchored to two separate anchors 303. In this regard, the anchors 303 provide attachment points for two primary upstream mooring cables 302. The upstream mooring cables 302 may be attached to the hydrokinetic device 300 with identical intercept angles 310. The two upstream mooring cables 302 inscribe a mooring angle 301. The centerline 311 of mooring angle 301 may be aligned and collinear with the most frequently occurring ocean current direction C. Additionally, the mooring angle 301 may be made large enough to encompass the vast majority of all ocean current directions that may occur at the deployment location.

The dual point mooring arrangement allows the hydrokinetic device 300 to have a fixed horizontal location 306 with little, or no lateral movement. That is, the hydrokinetic device 300 may yaw and change its azimuth angle, with little, or no lateral movement as the water current flow direction may change from time to time. Additionally, as the hydrokinetic device 300 yaws, it may likely experience a substantially constant, non-varying drowning force that is exerted by the mooring cables 302, by virtue of the identical intercept angle 310 of the two mooring cables 302, thereby not introducing a varying drowning force as described in reference to the triple point mooring system of FIG. 3C-1. Additionally, the hydrokinetic device 300 may be free to ascend or descend while maintaining mooring cables 302 taught without risk of mooring cable entanglement.

FIG. 4 shows an example of a mooring system with redundant safety lines, according to principles of the disclosure. In this arrangement, a hydrokinetic device 400 is attached to a plurality of anchors via a pair of mooring cable groups 401. Since each mooring cable group 401 includes a plurality of mooring cables, this arrangement may provide increased reliability and safety. Each of the mooring cable groups 401 preferably includes an equal number of mooring cables. However, one mooring cable group 401 may have more, or fewer mooring cables than the other mooring cable group 401.

FIG. 5 shows a perspective view of an example of an intermediary harness 500, according to principles of the disclosure. The intermediary harness 500 provides a connection interface between the downstream ends of the mooring cables at the point of connection to the hydrokinetic device 506. As seen, the intermediary harness 500 is configured to allow the hydrokinetic device 506 a freedom of rotation about both a pitch axis and a yaw axis. The intermediary harness 500 is further configured to facilitate alignment of the main rotational axis of the rotor with a free stream current direction of the water current, thereby maximizing energy conversion performance. The intermediary harness 500 is further configured to provide a termination point and an attachment point for the downstream end of the mooring cables, which remains substantially motionless as the hydrokinetic device 506 pivots in both pitch and yaw, thus extending the useful life of the mooring cables.

The intermediary harness 500 may include a yoke 501 that is attached (or mounted) to a hinge 503. The hinge 503 may include, for example, a cross-member, a cross bar, or the like. For instance, the hinge 503 may include a vertical member having a vertical axis 504 that is rotatably mounted to a pair of supports 502. The supports 502 may be affixed to, for example, a keel of the hydrokinetic device 506, or integrally formed with the keel. The hinge 503 may also include a horizontal member having a transverse axis 505 to which the yoke 501 is rotatably mounted. The yoke 501 and supports 502 may include, for example, hermetically sealed bearings, or other friction reducing devices that may resist the harsh ambient conditions in, for example, ocean applications.

As seen in FIG. 5, the yoke 501 is rotatable about the vertical axis 504 of the hinge 503, as well as the transverse (or horizontal) axis 505. Rotation about both the transverse axis and the vertical axis 504 allows the hydrokinetic device 506 to pitch and yaw, respectively, whilst the intermediary harness 500 remains in a generally fixed position and orientation.

FIG. 6 shows an example of an ocean farm array having of a plurality of hydrokinetic devices 600 moored by upstream mooring cables 601 to seabed anchors 602 which rest on a sea floor 604. Upstream mooring cables 603 extend to other neighboring hydrokinetic devices (not shown) in the ocean current farm array. The axis of the most commonly occurring ocean current flow direction is indicated by a centerline 605. Each sea bed anchor 602 may have attached to it two or more mooring cables used to restrain the hydrokinetic devices 600. Electrical and communication lines 606 (shown as dotted lines) may be attached to the upstream mooring cables 601. The electrical and communication lines 606 may include, for example, electrical wires, fiber optic lines, or the like. The lines 606 may be routed along and supported by the mooring cables 601 from the hydrokinetic device 600 to sea bed anchor 602, then to the next hydrokinetic device 600 and the next sea bed anchor 602, and so on.

FIG. 7 shows an example of electrical and communication lines 706 near the intermediary harness 500 that is attached to a hydrokinetic device 600. The electrical and communications lines 706 may be bundled together and connected near the nose section of the hydrokinetic device 600. The electrical and communications lines 706 may be attached to one or more of the cables 701, as seen in FIG. 7.

Referring to FIGS. 6 and 7 concurrently, the electrical and communications lines 606 collect the electrical energy and communication data from each hydrokinetic device 600 and transfer the electrical energy and communication data to a central collection point (not shown) within the bounds of the ocean current farm array prior to transmitting the electrical energy and communication data to an onshore (or offshore) location using one or more transmission lines (not shown).

In the preceding description, the electrical and communication lines 606 may not come in contact with the sea bed thus simplifying installation and maintenance and prolonging survivability. The electrical and communication lines 606 may be installed at the same time as the sea bed anchors and mooring cables are installed thus eliminating a separate construction step.

While the disclosure has been described in terms of exemplary embodiments, those skilled in the art will recognize that the disclosure can be practiced with modifications in the spirit and scope of the appended claims. These examples given above are merely illustrative and are not meant to be an exhaustive list of all possible designs, embodiments, applications or modifications of the disclosure. 

1. A mooring system for retaining one or more hydrokinetic devices, the system comprising: a hydrokinetic device that is configured to harness energy from a water current and generate electrical power; at least two anchors; and at least two mooring cables having upstream ends attached to the at least two anchors and downstream ends attached to the hydrokinetic device, wherein a centerline of a mooring angle is substantially aligned with a most frequently occurring water current flow direction.
 2. The system according to claim 1, wherein the mooring angle encompasses a majority of water current flow directions detected at the location over a predetermined period of time.
 3. The system according to claim 1, further comprising: an electrical line that is attached to one of the at least two mooring cables.
 4. The system according to claim 1, further comprising: a communication line that is attached to one of the at least two mooring cables.
 5. The system according to claim 1, further comprising: an intermediary harness that provides a connection interface between the at least two mooring cables and the hydrokinetic device.
 6. The system according to claim 5, wherein the intermediary harness comprises: a yoke that is configured to pivot about a transverse axis.
 7. The system according to claim 5, wherein the intermediary harness comprises: a hinge that is configured to rotate about a vertical axis.
 8. The system according to claim 6, wherein the intermediary harness further comprises: a hinge that is configured to rotate about a vertical axis.
 9. A mooring system for retaining one or more hydrokinetic devices, the system comprising: at least two mooring cables having upstream ends attached to respective anchors and downstream ends attached to a hydrokinetic device, wherein a centerline of a mooring angle between the at least two cables is substantially aligned with a most frequently occurring water current flow direction.
 10. The system according to claim 9, further comprising: an intermediary harness that provides a connection interface between the at least two mooring cables and the hydrokinetic device.
 11. The system according to claim 10, wherein the intermediary harness comprises: a yoke that is configured to pivot about a transverse axis.
 12. The system according to claim 10, wherein the intermediary harness comprises: a hinge that is configured to rotate about a vertical axis.
 13. A mooring system for retaining a hydrokinetic device, the system comprising: a yoke that is configured to support a mooring cable and pivot about a first axis; and a hinge that is configured to support the yoke and connect to a support on the hydrokinetic device, the hinge being further configured to rotate about a second axis.
 14. The system according to claim 13, wherein the first axis is substantially perpendicular to the second axis.
 15. The system according to claim 13, wherein the yoke is configured to support at least two mooring cables.
 16. The system according to claim 13, wherein the hinge comprises a cross bar.
 17. The system according to claim 13, further comprising: at least two mooring cables having upstream ends attached to anchors and downstream ends attached to the yoke.
 18. The system according to claim 17, wherein a centerline of a mooring angle formed between the at least two mooring cables is substantially aligned with a most frequently occurring water current flow direction.
 19. The system according to claim 18, wherein the mooring angle encompasses a majority of water current flow directions detected at a location over a predetermined period of time.
 20. The system according to claim 17, further comprising an electrical line attached to one of the at least two mooring cables.
 21. The system according to claim 17, further comprising a communication line attached to one of the at least two mooring cables. 